Galvanic cells may generate large quantities of gas under certain conditions during use. Since these cells are required to be tightly sealed at all time in order to prevent loss of electrolyte by leakage, high internal gas pressures may develop. Such pressures may cause leakage, bulging or possible explosion of the cell if not properly vented. If a vent valve is employed, it generally is resealable in order to avoid drying out of the electrolyte over the life of the cell and to prevent ingress of oxygen from the atmosphere which can cause wasteful corrosion of the anode.
In the past several different types of resealable pressure relief vent valves have been used for releasing high internal gas pressures from inside a sealed galvanic cell. One type of valve that has been commonly used consists basically of a valve member, such as a flat rubber gasket, which is biased into a sealing position over a vent orifice by means of a resilient member, such as a helical spring. The resilient member or spring is designed to yield at a certain predetermined internal gas pressure so as to momentarily relieve the seal and allow the gas to escape through the vent orifice.
Another type of resealable vent is disclosed in U.S. Pat. No. 3,451,690 to Richman issued on Dec. 10, 1968. In this vent, a flat elastomeric seal gasket overlies the vent opening and is retained in place by a resilient terminal cap on the top of the cell. This vent operates in basically the same manner as the vents previously described.
In U.S. Pat. No. 3,664,878 to Amthor issued on May 23, 1972, a resealable vent is disclosed which comprises a resilient deformable ball of elastomeric material positioned to overlie a vent orifice provided within the cell's container. A retainer means is positioned over the resilient ball for maintaining the ball in place over the vent orifice and in contact with a valve seat provided around the peripheral edge portions of the vent orifice and for compressing and deforming the resilient ball into a flattened configuration forming a normally fluid-tight seal between the flattened ball and the valve seat. The resilient ball is capable of undergoing further temporary deformation upon the buildup of a predetermined high internal gas pressure inside the container so as to momentarily break the seal and allow gas to escape through the vent orifice.
A major problem encountered with resealable pressure relief vent valves of the types just described is that they are bulky and/or difficult to incorporate into the cell assembly. Furthermore, these pressure relief vent valves are expensive to manufacture and most are not adaptable for incorporation into miniature size cells. In addition, some of the prior art resealable vents as exemplified by the foregoing patents are not suitable for low pressure venting.
Alternates to high pressure resealable vent means are fail safe venting systems as illustrated in U.S. Pat. Nos. 3,218,197 and 3,314,824. Specifically in the '197 patent a venting means is disclosed in which the seal gasket has a thin section that will rupture or "blow-out" at a predetermined high pressure buildup within the cell. The difficulty with this type of venting means is that for small diameter cells it is difficult to obtain consistency in the thickness of the "blow-out" section of the gasket using conventional manufacturing techniques. In the '824 patent a puncture-type safety seal is disclosed which comprises a spring washer positioned within the cell's seal assembly and a radially acting toothed puncture washer. The teeth of the washer slide relative to the spring washer when the spring washer is subjected to internal pressure so that at a predetermined gas pressure buildup, the teeth of the washer will puncture the seal's gasket thereby providing a vent passage. This type of venting means requires several component parts, is rather expensive to make and assemble, and is not suitable for small diameter cells.
An inexpensive low pressure resealable vent closure is disclosed in U.S. Pat. Nos. 4,020,241 and 4,063,902 filed in the name of Henry Heinz, Jr. Specifically, a galvanic cell is disclosed having a resealable vent closure consisting of a resilient elastomeric sponge gasket disposed and compressed between the cover of the cell and the upper wall of the cell's container and designed to vent low pressure gas buildup along the cover-gasket interface and/or container-gasket interface.
U.S. Pat. No. 4,079,172 discloses sealed galvanic dry cells having at least one gas venting passage disposed at the interface of the top surface of the cover and then curled over rim of the container. The passage is defined as being a recess in the cover disposed below the curled over rim and/or a notch in a portion of the curled over rim.
As discussed above, resealable, high pressure relief vent valves are generally bulky and/or difficult to incorporate into a cell assembly, blow-out type safety vents are not suitable for small cell applications, while low pressure vent means for some cell systems may not adequately and sufficiently prevent loss of electrolyte through leakage or prevent ingress of oxygen from the atmosphere which could cause wasteful corrosion of the anode.
It is, therefore, an important object of this invention to provide a compact and economical high pressure vent for use in a galvanic cell.
Still another object of this invention is to provide a high pressure vent for galvanic cells which requires a small number of parts and which is, therefore, easy to assemble and inexpensive to manufacture.
Another object of this invention is directed to a galvanic cell in which a first arc portion between about 150.degree. and 190.degree. of the top peripheral edge of the container is turned or curled over the container's closure means so that when a predetermined high pressure build-up develops in the cell, the pressure will cause the closure means to tip or tilt about the diametral axis formed between the first arc portion and the remaining second arc portion so as to produce a vent passage at the interface of the container and the closure means proximal the remaining second arc portion of the top peripheral edge of the container.
The foregoing and additional objects will become more fully apparent from the following description and the accompanying drawings.